Ion exchange polymer electrolyte membranes and their dispersions in liquid medium are used for membrane-based electrochemical systems, such as fuel cells and water electrolysis systems. Typically, electrochemical systems are categorized into acidic and alkaline systems based on their operating environments. Acidic electrochemical systems are operated under low pH and typically use a cation (or proton) exchange polymer electrolyte. In cation exchange polymer electrolytes, anionic functional groups (e.g., sulfonic acid group) are tethered in polymer backbones or polymer side chains to conduct protons. Alkaline electrochemical systems are operated under high pH and typically use an anion (or hydroxide) exchange polymer electrolyte. In anion exchange polymer electrolytes, cationic functional groups (e.g., quaternary ammonium groups) typically are tethered in polymer backbones or polymer side chains to conduct hydroxide ions.
Acidic membrane-based electrochemical energy systems are popular, primarily due to the commercial availability of perfluorosulfonic acid. The commercially available perfluorosulfonic acid polymers have good proton conductivity (˜100 mS/cm at 30° C.) as well as good chemical, mechanical, and thermal stability. The perfluorinated polymer electrolytes have significant advantages over hydrocarbon-based polymers due to their higher oxygen permeability, hydrophobicity, low catalyst poisoning, ideal three-phase interface, and ability to create a porous electrode structure. Such acidic systems, however, exhibit low efficiency of the oxygen reduction reaction of the electrocatalysts. As a result, expensive platinum-based catalysts typically are required for good cell performance.
For alkaline electrochemical systems, no industrial standard anion exchange membranes and liquid dispersions are available. Cationic group-functionalized polyaromatic anion exchange membranes have potential for use in electrochemical energy systems, particularly alkaline systems, because of their conductivity, film formability and high chemical stability. However, these polyaromatic anion exchange membranes are not readily incorporated into typical solvents used for such systems, particularly alkaline electrochemical systems. There exists a need in the art for compositions that comprise cationic group-functionalized polyaromatic polymers and dispersion media that can be used in electrochemical systems, such as alkaline and acidic electrochemical systems.